Ni-Ru/CeO2 Catalytic Hydrothermal Upgrading of Water-Insoluble Biocrude from Algae Hydrothermal Liquefaction

Hydrothermal liquefaction (HTL) of algae is a promising crude bio-oil (biocrude) production technology, which can convert wet algae into water-insoluble biocrude and other coproducts. In this work, algae HTL at 350°C and 20 min was conducted to obtain water-insoluble biocrude (B 1 ), which was then hydrothermally upgraded at 450°C, 60 min, or with added H 2 and/or homemade catalyst (i.e., Ni-Ru/CeO 2 or Ni/CeO 2 ) for the first time. The characteristics (e.g., yield, elemental component, energy recovery, and molecular and functional group compositions) of upgraded water-insoluble biocrude (B 2 ) as well as light biocrude thereof were analyzed comprehensively. The results show that Ni-Ru/CeO 2 +H 2 led to the highest yield and HHV (higher heating value), the best elemental compositions quality of B 2 , and the largest fraction and the best light of light biocrude in B 2 . Ni-Ru/CeO 2 +H 2 had good catalytic desulfurization effect and could transform high-molecular-weight compounds into low-molecular-weight compounds in B 1 upgrading. At the condition above, 46.2% of chemical energy in the initial algae could be recovered by B 2 , while average 54.9% of chemical energy in B 2 was distributed in its light biocrude (hexane-soluble) portion. On the whole, Ni-Ru/CeO 2 +H 2 can be considered as the optimal additive in all tested cases.